The present invention relates to bone cement compositions used in the bonding or fixing of implant materials, as well as in the strengthening of damaged natural bone. The present invention further relates to bone cement compositions having bioactive properties.
Bone cement compositions are useful in the bonding or fixing of an implant material, as well as in the strengthening of damaged natural bone. Such applications are particularly useful in the areas of orthopedics, dentistry and related medical disciplines. The field of orthopedics deals with bone defects due to fracture, bone tumors, and other diseases of the bone. Treatment may require surgical resection of all, or part, of a bone. In dentistry applications, a defected jawbone may result from extraction of a tooth, cancer or other diseases. An implant material is useful in repairing or reconstructing the bone remaining after the resection of such bone defects. Implant materials used during such procedures are frequently comprised of metal, ceramics and polymers.
It is advantageous for the implant material to be able to quickly adapt in order to embed and fix in the repaired site. To facilitate this, the implant material must either be ground or worked into a shape adapted to the repair site. However, it is difficult to perform this work with the high precision necessary. Because of the limitations of implant materials, bone cement is often used with the implant material in order to bond and affix the implant to the remaining, living bone. For example, polymethyl methacrylate (PMMA) has been widely used with hardware instrumentation in orthopedics.
Although conventional PMMA bone cement has been used in orthopedic surgery for over 40 years, it is far from ideal because 1) it does not encourage bone in-growth, 2) it is a weaker implement than bone cortex, and 3) it has a high exotherm and monomer toxicity. Research, focusing on bioactive bone cements, has been ongoing to modify or replace conventional PMMA bone cement to eliminate or reduce these limitations.
Sogal et al. modified PMMA by adding hydroxy apatite (HA) powder. It is also known to add bone particle and growth hormone to PMMA. Japanese Patent Publication No. 42384/1979 discloses a biocement comprised of a combination of polymethyl methacrylate (PMMA) and K2Oxe2x80x94Na2xe2x80x94CaOxe2x80x94MgOxe2x80x94SiO2xe2x80x94P2O5 crystallized glass powder.
Although some improvement has been made to conventional PMMA, fundamental problems remain with the methyl methacrylate (MMA)/PMMA system. Brown et al. developed a new type of bioactive calcium phosphate cement originally used in dentistry in the 1980s. Although this bioactive cement showed good bioactivity with bone, its weak mechanical properties made it unsuitable for use in repairing weight-bearing bones. In addition, the long setting time of this cement made it impractical for use in many applications.
Recently, a number of alternatives to the basic MMA/PMMA system have been explored, such as bioactive filler-Bis-GMA systems. Japanese Patent Prepublication No. 503148/1987 and U.S. Pat. No. 5,527,386 disclose this type of bioactive cement, comprised of a combination of 2,2-bis[4-(3-methacryloxy-2-hydroxy propoxy) phenyl] propane (Bis-GMA) base monomer and apatite powder with bioglass powder added as an optional component. Another example of developing bioactive cement systems is British HA reinforced poly (ethyl methacrylate)/n-butyl methacrylate (PEMA-nBMA). However, these types of bioactive bone cements are not yet satisfactory with respect to bonding to living bone, bond strength, mechanical strength, and chemical stability of the hardened cement core. Bis-GMA cement is especially limited in that it displays poor handling properties and potential increases in stresses in vivo due to its high modulus. However, Bis-GMA cement does display significant bioactivity. PEMA-nBMA is especially limited in that it has an unacceptably low creep resistance when unfilled.
It has been speculated that minimally invasive bone cement injection has significant clinical potential for use in the treatment of vertebral body fracture or to stabilize osteoporosis. Bioactive bone cement and other cements can gradually form micro cavities from the outside to the inside after the cement sets. The use of conventional PMMA bone cement and related derivatives is limited, as these cements are not suitable for use in spinal surgery.
The invention is a bioactive bone cement composition including a powder component and a liquid component. The powder component comprises strontium-containing hydroxy apatite, and the liquid component comprises Bisphenol A diglycidylether dimethacrylate resin. These two components are formulated to create a settable fluid substance when mixed together.
The bioactive bone cement can alternatively be in the form of a two paste component system in which the first paste component is comprised of strontium-containing hydroxy apatite, Bisphenol A diglycidylether dimethacrylate resin and a polymerization initiator, and the second paste component is comprised of strontium-containing hydroxy apatite, Bisphenol A diglycidylether dimethacrylate resin, and a polymerization accelerator. The first and second pastes are formulated to create a settable paste substance when mixed together.